Oxide on Steam Generator Tube Materials in Alkaline Solutions

In spite of much effort to reduce the material degradations, stress corrosion cracking (SCC) is still one of important problems to overcome. Cracks can initiate and propagate through unavoidable breakdowns and alterations of the surface oxide that forms naturally on Alloy 600 in an aqueous solution. Characterisation of the surface oxide properties would therefore be helpful for elucidating PbSCC mechanism. Secondary water pH levels that reveal a shift from acidic to alkaline states can affect SCC behavior to spread extensively in crevices. The pH depends on the water chemistry control, the water chemistry in crevices, plant-specific condition and so on. Specific chemical species accumulate in crevices leading to a specific condition of crevice chemistry. One of these chemical species is lead. It is one of the most deleterious species in reactor coolants that cause SCC in alloys. The lead in a solution is presumed to modify the oxide property and hence induce SCC susceptibility. However the PbSCC phenomenon could be reduced if this type of modification can be avoided through the discovery of a suitable inhibitor. In the present work, the oxides were investigated in alkaline solutions in the presence/absence of lead at 315 .deg. C using TEM, EDS and XPS. Moreover SCC behavior was compared in aqueous solutions with and without lead